Here's one method . . .
1. Create the print as you have, with no regard for exact position of the negative on the paper.
2. Crop the print to the appropriate size and orientation, eliminating the white border.
3. Mount the print on a board of a color and texture that compliments the picture.
4. Sign the board under the print in pencil, or sign the print directly.
5. Enjoy your print for the next 150 years.